Studies on the induced biosynthesis and surface expression of the molecule bearing Lyt-1 alloantigen are being extended further to the molecular level with the help of two well-defined mitogen-responsive T-cell lymphoma clones (derived from LBRM-33): one responding to stimulation in vitro with mitogen alone (5A4) and the other requiring mitogen plus IL-1 as inductive signal for de novo synthesis of both IL-2 and Ly-1. Inductive regulation and inhibition of sIg:k biosynthesis and cell surface expression is being defined in two clones described from the cell line ZOZ.3, one responding to stimulation in vitro with purified IL-1 and recombinant interferon-gamma by de novo synthesis and cell surface expression of sIg:k, the other failing to express these molecules at the cell surface after induction. Additional studies will determine possible regulatory effects of B-cell differentiative molecules (e.g., IL-1, interferon-gamma) on the variable expression of kappa gene products in isolated kappa-gene transfected myeloma clones. The functional participation of different Ly-5 isoforms is being defined in the induction of Lyt-1 expression by the T-cell lymphoma clones above, in the induction of sIg:k expression by B cells, and in the development of two genetically defined murine lymphoproliferative disorders, 1pr/1pr and gld/gld, that are found to exhibit expression of an aberrant Ly-5 isoform. (LB)